1. Field of the Invention
The present invention relates to a process for preparing an osteogenesis promoting substance, which is useful as a bone repairing agent and a bone grafting agent in the field of surgery, orthopedic surgery and dentistry.
2. Description of the Prior Art
Conventionally, bone grafting in a living body is performed generally by autografting with a bone of the patient himself. However, the bone thus available for autografting is limited in quantity, while the patient must undergo surgery twice for the removal of the bone and the transplantation thereof and therefore suffers pain.
To overcome the drawback of autografting, it has been attempted to use a demineralized powder of organic matrix from the bone of a mammal (hereinafter referred to as "demineralized bone powder") to be implanted in the living body to cause the formation of an autogenous bone (Glowacki et al., Lancet, May 12, 1981). The demineralized bone powder contains several kinds of local osteogenesis promoting substances. When the powder is implanted in the living body, these osteogenesis promoting substances are systematically combined with one another at each step of ossification to for a new bone. First, granulations are formed around the particles of the demineralized bone powder through a vital reaction. Subsequently, mesenchymal cells in the living body are drawn to the surfaces of the particles of the powder by a chemotactic factor present in the bone powder and are differentiated into cartilage cells by a differentiation promoting factor present in the powder. When blood capillaries are formed in the granulation tissue, the cartilage cells die. The mesenchymal cells are differentiated into osteoblasts by a factor released from the cartilage cells and a factor released from the powder. The osteoblasts secrete collagen into the interstices between the particles of the bone powder, further calcifying the secreted collagen, with the result that a normal bone is formed in the interior of the granulation tissue. The bone thus formed undergoes a metabolic turnover as a normal bone.
However, the demineralized bone powder forms a new bone in the living body only in the case where the powder prepared from a bone from a species same as the recipient is implanted. A satisfactory bone will not always be formed owing to the inherent antigenicity in the case where the powder is prepared from a bone from a species different from the recipient. There is a limited availability of material when the powder is prepared from a bone from a homozoic species to produce a bone grafting agent, especially the species is human being. In view of the above problem, an attempt has been made to synthesize the osteogenesis promoting substances. The synthesis includes extracting and purifying the osteogenesis promoting substances, determining the amino acid sequence thereof, and synthesizing the substances by a gene recombination or the like [Wang, E.A. et al., Proc. Natl. Acad. Sci. USA, 87, 2220(1990); Bentz, H. et al., J. Biol. Chem., 264, 20805(1989); Luyten, F.P. et al., J. Biol. Chem., 264, 13377(1989); Sampath, T.K. et al., Calcif. Tissue Int., 46, Suppl. 2, A46(1990)].
An isolation method of an osteogenesis promoting substance is disclosed, for example, Methods in Enzymology, 146, 294-312 (1987) and in Journal of Biomedical Materials Research, 24, 639-654 (1990).
A normal ossification is conducted by the action of many osteogenesis promoting substances which are present in the bone matrix and systematically combined with one another, whereas a single osteogenesis promoting substance obtained as above affords remarkably weak or no osteogenic activity.